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Image of the Week

Asteroids in Gaia

Apart from providing a huge catalogue of almost 1.7 billion stars, Gaia now also serves the solar system community with its first survey of asteroids, released on 25 April with the Gaia second data release. In this image of the week a short history of Gaia's asteroid survey is given.

Before launch in 2013, an illustration was published on Gaia's expected advantage to probe the asteroid blind spot (Illustration on 22/10/2013: Gaia will probe the asteroid blind spot). Gaia operates from the second Lagrange point L2 of the Sun-Earth system, a point that moves along with Earth while Earth orbits the Sun. From this location, Gaia is capable to discover small bodies orbiting the Sun inside the Earth's orbit. From Earth, these objects are mostly unobservable. An artist impression animation shows what Gaia can observe with respect to what can be observed from Earth.

Once Gaia started it's routine operations, time came to test the processing pipeline for asteroid detection. Eight months of Gaia data and a sample of 50,000 asteroids were used to test the detection efficiency of the software in the Gaia processing pipeline. More information on this test can be found in this image of the week story of 31/07/2015: Asteroids all around (or the accompanying story: Gaia's asteroid detections).

With Gaia's first data release, the precise astrometry of the stars started to make observation of asteroids through stellar occultation methods more easy. Only a few days after the release of Gaia DR1, the predicted shadow path of the stellar occultation by minor planet (671) Carnegia was updated using the more precise position of the to-be-occulted star from Gaia DR1. This allowed for an amateur astronomer in New Zealand to successfully observe this occultation (21/10/2016: First post-Gaia asteroid occultation success: a feedback from amateur astronomy).

While the Gaia Data Processing and Analysis Consortium was working towards the second data release, a short story on how Gaia reveals the composition of asteroids was published, discussing what the data from cycle 1 of the processing revealed and to show the potential of Gaia with respect to this type of analysis (24/04/2017: Gaia reveals the composition of asteroids).

To allow for quick follow-up of potentially newly discovered solar system objects, a follow-up network for solar system objects was started listing all these potential asteroid discoveries made by Gaia waiting for a confirmation by follow-up observations (24/01/2017: Gaia follow up network for solar system objects). To help the community plan for observations, the Gaia-GOSA service offers a forum to discuss and plan observing campaigns and gives an overview of interesting asteroids in need for follow-up (24/11/2017: Gaia-GOSA service).

The impact of again more precise positions of stars given by Gaia's data release 2 was illustrated with the pre-release of a few Gaia DR2 stars to allow for improving the predicted occultation path by asteroid Chariklo. More information on this stellar occultation and Gaia's impact can be found here: Chariklo stellar occultation follow-up.

In the below figure, the orbits of this full set of 14,099 asteroids are given each with a very specific colour code: coloured by perihelion distance (on the left), coloured by eccentricity of the orbit (in the middle) or coloured by the albedo of the asteroid (on the right).

Figure 2a: Plot of the orbits of the asteroids in Gaia Data Release 2. Left image is coloured according to perihelion distance (the distance of the asteroid in its orbit where it is closest to the Sun). Center image is coloured following the eccentricity of the asteroids. Right image is coloured following the albedo of the asteroids. ESA/Gaia/DPAC, P. Tanga

Figure 2b: Zooms of the plot of the orbits as shown in Figure 1a. Left image is coloured according to perihelion distance. Center image is coloured following the eccentricity of the asteroids. Right image is coloured following the albedo of the asteroids. ESA/Gaia/DPAC, P. Tanga